A conventional receptacle 1 as shown in FIG. 3(A) employs a split sleeve 2. In this optical receptacle 1, a stub 4 with an optical fiber is fixed to a stub holder 3 by press-fitting or through an adhesive. The stub 4 with an optical fiber is held in the split sleeve 2 having sufficient elasticity, and the split sleeve 2 is closed within a clamping allowance to hold the stub 4.
An optical connector ferrule 7 is inserted from an opening part 5a of a split sleeve cap 5 of the optical receptacle 1, and the optical connector ferrule 7 and the stub 4 are aligned precisely and concentrically by the split sleeve 2. An optical receiver/optical transmitter 6, provided with a photosemiconductor 6a, a lens 6b, and a holder 6c for holding the photosemiconductor 6a and the lens 6b, is arranged on a back side of the optical receptacle 1. The optical connector ferrule 7 and the stub 4 with an optical fiber are aligned precisely and concentrically by the split sleeve 2, to thereby connect optically the optical receiver/optical transmitter 6 and an optical fiber 7a in the optical connector ferrule 7 through the stub 4 with an optical fiber.
The optical receptacle 1 shown in FIG. 3(A) is most orthodox and has an initial style devised to be connected concentrically with an optical connector by using the stub 4. Recently, reduction in size of a transmission apparatus itself is highly needed, and a reduction in length of an optical receptacle to be used for the transmission apparatus is strongly demanded. In order to achieve this reduction in length, various forms of optical receptacles are employed. For example, as shown in FIG. 3(B), Patent Document 1 (see the list below) discloses a small optical receptacle 1a constructed of four components and having a structure including a holding ring 8 press-fitted between a split sleeve 2 and a split sleeve cap 5 such that a short stub 4 with an optical fiber can be aligned precisely and concentrically so that even the short stub 4 is held strongly by the split sleeve 2 and is not loosened.
Further, as shown in FIG. 3(C), Patent Document 2 discloses a small optical receptacle 1b including a split sleeve 9 which is split not across the entire sleeve but is split only on a side where an optical connector ferrule 7 is inserted. It is not split on the side of a stub 4. The stub 4 is bonded and fixed to the split sleeve 9. As described above, a full length of the stub 4 with an optical fiber is reduced, and the stub 4 can be aligned precisely and concentrically. In this optical receptacle 1b, the stub 4 is fixed to a stub holder 3 by press-fitting or through an adhesive, and a special split sleeve 9 as described above is fixed to the stub 4. Further, a split sleeve cap 5 is fixed so as to cover the split sleeve 9. Thus, the optical receptacle 1b has four components in total.
Meanwhile, Patent Document 3, by the inventors of the present invention, discloses: an optical fiber capillary having an inner hole with a surface roughness Ra value of 0.1 μm to 0.5 μm for securing concentricity between the inner hole of the optical fiber capillary and an optical fiber; and a stub with an optical fiber using the optical fiber capillary.
Further, Patent Document 2 and Patent Document 4 each disclose an optical receptacle having an outer periphery surface of a ferrule and an inner periphery surface of a sleeve each with a surface roughness Ra value of 0.2 μm or less for securing an insertion property of the ferrule into the sleeve.
Patent Document 1: JP-A-10-332988
Patent Document 2: JP-A-2003-107288
Patent Document 3: JP-A-2003-149502 (US 2003095753 A1)
Patent Document 4: JP-A-2003-222764
In the conventional optical receptacle 1 described above, the stub 4 with an optical fiber is fixed to the stub holder 3, and the split sleeve 2 is used as a component for aligning the optical connector ferrule 7 and the stub 4 concentrically. However, the split sleeve 2 only holds, and does not fix, the stub 4. Thus, in order to prevent removal of the stub 4 with an optical fiber when the optical connector ferrule 7 is inserted and pulled out, the split sleeve cap 5 is required. As a result, a minimum of four components are required for constructing the optical receptacle 1. Those components are all essential elements for constructing the optical receptacle in this form, and the number of components cannot be reduced further. Thus, the conventional optical receptacle has a problem of difficulties in cost reduction.
Further, for realizing a reduction in size of an optical device, the stub 4 with an optical fiber is preferably as short as possible for mounting a high-density light guide member. However, a short stub 4 with an optical fiber reduces the holding force of the split sleeve 2. In the case where the optical connector ferrule 7 is inserted into the split sleeve 2 and a horizontal load is applied thereto, the optical connector ferrule 7 and the stub 4 with an optical fiber cannot maintain concentric alignment. An angular shift occurs between an optical axis of the short stub 4 with an optical fiber and an optical axis of the optical connector ferrule 7, and precise and concentric alignment cannot be maintained. Thus, the stub 4 with an optical fiber cannot be reduced in length further.
The optical receptacle of Patent Document 1 has achieved size reduction, but requires a holding ring 8 for reinforcement for stably maintaining a positional relationship between the optical axis of the short stub 4 with an optical fiber and the optical axis of the optical connector ferrule 7 for a single mode optical fiber. As a result, the optical receptacle has a problem in that the number of expensive components increases.
The optical receptacle of Patent Document 2 has achieved size reduction, but requires the special split sleeve 9 having a slit partway. The optical receptacle requires more complex working, and a cost increase cannot be prevented. Further, this optical receptacle requires the split sleeve cap 5 as in the conventional optical receptacle 1. Thus, the number of components cannot be reduced further.